The present invention relates to clutches, and in particular to a solenoid activated spring clutch.
Wrap-down spring clutches are used in a wide variety of applications, such as the adjustable hospital bed disclosed in my copending U.S. patent application Ser. No. 147,217, filed May 6, 1980, entitled DRIVE UNIT FOR ADJUSTABLE BEDS, which is hereby incorporated by reference. These spring clutches typically include a driving drum with a coil spring connected therewith, a friction or a clutch drum which is positioned concentrically within the spring, and an activator, such as clamping arms, or the like, which selectively cause the free end of the spring to wrap constrictingly down against the periphery of the clutch drum for transmitting rotation from the driving drum to the clutch drum.
Heretofore, activators for such clutches have been unable to both engage quickly and initiate a secure spring wrap-down which would not inadvertently slip during power transmission. These clutches also tend to intermittently engage and disengage or "chatter" during spring wrap-down. The forces which are typically required to initiate and sustain clutch engagement in such devices are very high in comparison to the power which the clutch is capable of transmitting, thereby affording a rather inefficient and unattractive clutching mechanism. Further, these spring clutches have a complicated design with the internally located activators, such that both the manufacturing and maintenance costs are relatively high.